Measuring the photometric brightness or color of light sources that are either intermittently or repetitively pulsed over time requires special techniques to assure accuracy. These light sources include florescent lights, xenon lamps, cathode ray tube (CRT) screens, or in general light sources that appear to have constant intensity to an observer but are in actuality pulsing faster than human senses can perceive.
The simplest approach is to integrate or average brightness or frequency measurements over a very large number of cycles or pulses (i.e., 100 or more). This method, however, can take a great deal of time, especially if the pulse repetition rate is low, and can result in errors if either the pulse-amplitude, the pulse-repetition rate or the ambient light intensity or frequency are not constant.
Another technique is to synchronize the electronics of the light source with the electronics of the measuring instrument (which may be either a photometer, radiometer, spectroradiometer, or colorimeter), so that an exact integral number (N=2, 3, 4, etc.) of pulses are measured. This technique is far more complex to execute, generally requires knowledge of the timing characteristics of the light source before the measurement is begun, and is subject to large errors if not executed properly.
If the measuring instrument were not properly synchronized with the light source several errors would occur. The "worst-case" example would be a multichannel-array spectroradiometer trying to measure a synchronous single pulse of light. Depending on the timing between the light pulse and the photodetector array in the spectroradiometer, the pulse could occur when some or all of the individual photodetectors were not ready to receive light which would produce an erroneously low reading from these photodetectors, which would result in large errors in the measurement data.